In the noon of day is when they have this event were condemed criminals fought each other until death and the winner fought until he himself was killed. What happened to the ultimate winner is unknown maybe he was let go or allowed to live another day.
How you became a Gladiator well you had to be a crimanials, slaves, or prisoners of war and if you had the phyisical and emontial make up for one. They had no choice in the matter there lives were in the hands of another not themselves
The life of gladiators were harsh but not always sometimes they lived better than most commoners in terms of foodhousing, and medical attention.
http://dethhome.brooklyn.cuny.edu/classics/gladiatr/index.htm